Phase composition and wear behavior of NiTi alloys

This study deals with the wear behavior of two NiTi shape memory alloys, one of them being martensitic, the other one austenitic at room temperature. Wear tests have been conducted with a disk-on-block geometry. The block was made of the NiTi alloy, whereas counterface disk materials were AISI M2 high-speed steel and a WC-Co hardmetal. From the evolution of the friction coefficient and temperature during the tests and from the characterization of the wear debris and traces, it has been possible to identify the main wear mechanisms. In the wear tests involving the M2 steel disk, both NiTi alloys display a transition, as a function of the applied load, from a mainly oxidation regime to a more complex situation, in which oxidation wear is accompanied by delamination of metallic alloy fragments. Higher wear rates of the shape memory alloys have been observed for the NiTi/WC-Co coupling. In this case, a transition from a mainly delamination wear to a regime featuring a mixture of delamination and oxidation wear has been observed.